Data compression is a technology to efficiently store data in a smaller storage space. For this, a technology to apply a specific algorithm to original data and generate compressed data together with information to identify the kind of the compression algorithm is widely used. Generally, the technology to generate such compressed data is provided from a database management system such as Oracle, SQL-server and DB2. Such a database management system forms particular columns of the data table having a high occurrence frequency as a symbol table by assigning a symbol, for example, a number or a character to each of the columns, and compresses the columns using the symbol table.